Traveling wave coupler



2 Lona.

H. M. STROBEL TRAVELING- WAVE COUPLER Filed ApIfl 12, 194] Couplng .Sczan of Line.

INVENTOR.

Mm.m`

Oct. 22, 1946.

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lulu

Osc. 1

to the art. One such method of energy collection uses two collecting plates, one on each side of the middle position of the stream, so that when the waved stream of charged particles impinges upon the plates, it charges rst one plate and then the other in alternate sequence. This alternating charging action can be used to energize an oscillating circuit.

The method of using the lield of a` traveling wave to vdeflect moving charged particles gives many advantages over known systems. Brief refcillator, or may be energized by the output of the high-frequency collector I2.

erence to some of these advantages may be made.' It will be noted that Vfor a given strength of eld in the traveling wave, the amplitude of deflection of the stream can be made as large as desired simply by increasing the length of the coupling section of the transmission line. Also, the amount of power that can be controlled is not limited by the usual considerations of physical Vsize of the apparatus. Further, very high frequencies can be generated'or'amplied without encountering the many difficulties inherent in othersystems wherein the physical size of the apparatus imposes severe limitations. Other advantagesoi the invention will be evident from the more detailed description that follows.

More particularly, the invention consists in the system and method hereinafter described, illustrated'in the accompanying drawing and defined inthe claimshereto appended, it being understood that various changes in form, arrangement and details both of circuits and of method within the scope of the claims may be resorted to withu outl'departing from the spirit .or sacricing any of the vadvantages of the invention.

` Aclearer. understanding ofthe operation Yof the invention and its improvement over known methods can be obtained by reference tofthe followinggures andthe descriptions relating thereto- 4'Figure 1 shows ablock diagram of the principal elements of the traveling wave coupler Vused as an amplifie'rifor' generating high-frequency currents. Figure 2 shows Va circuit diagram of a high-frequency amplifier embodying the principles of the invention, `with a graphical representation of the traveling wave in the coupling section- Figure 3 shows a diagram of a travelingwave coupled oscillatonl wherein the output energy of thev oscillator is' also used to energize the coupling section.'

Y Figure 4 shows a circuit'diagram of a traveling wave coupled oscillator' in vwhich the conducting members which guide ,the traveling wave are shown as of the coaxial type;v

Figure 1 is a blockdia'gramshowing the main elements of the wave coupler. Block I represents Va gun for creatingohigh' velocity charged particles, such` as electrons.' In what follows, it will be assumed that the charged particles used are electrons, although it will be obvious that this fsf'not, a necessary restriction. l Blockl II represents the coupling section, wherein the electrost'a'.tic field of the. traveling waveand the electrons of the electron stream are coupled together, so that the Wave eld displaces the electrons.V Block 12 represents a high-frequency collector for collecting Vhigh-frequency energy from` the waved stream'of electrons. Block `I3 represents the load' which utilizes 'the energyucollected by the high=frequ`ency collector I2. Block I4 shows the high-frequency energizer which energizes the transmission line of the coupling section II, and thus propagates a traveling wave of suitable mode throughthejcoupling section II. The high frequency energizerltmayfbean independent os:

In the operation of the traveling wave coupler, the electron gun I D directs a high velocity stream of electrons between the conducting members that form the transmission line of the coupling section I I. The transmission line consists 0f such members or medium as will serve to guide or propagate an electromagnetic wave alonga given path so that the traveling wave, ortransverse electrostatic neld component thereof, can be coupled to the electron stream. A conventional type of transmission line consists of two spaced parallel wires. In order that a traveling wave should be formed when the transmission line is energized at the head of the coupling section, it is necessary that reflected waves be kept at a mini; mum. -As is well known in the art, no reilected waves will occur if the transmission line is of innite length, or if thelineislterminated in a load impedance which is equalto the characteristic impedance of the line. In Figure 1, iffthe Aload impedance I3 is made equal to or matchedjwith the characteristic impedance of the coupling section I I, the conditions of no reflection will be satisfied. By energizing the head of the couplingA section II from an energizing source I 4, an elec-'A tromagnetic wave iscaused to travel along4 the coupling section towards its terminating load. The voltages, and theelds that result, which are applied to the head'of Vtheicoupling section are alternately of positive and negative polarity at some given frequency. The resulting electrostatic' elds will be substantially perpendicular to the surfaces ofthe conducting members and perpendicularto the direction'of motion of the travel-- ing wave. By directing, the electron stream in the direction.v of the traveling wave'v or between the conducting members which guide the wave,`

the electrons can be made to travel along theV coupling section I Iatsubstantially the same ve-v locity as the traveling wave, so that the traveling electrostatic iield has a greatly increased intervalw of time toV act upon and so displace the electrons laterally.Y Y

`*Still referring to Figure 1, if the high-frequency energizer I4 for the coupling section II isvan oscillator, the transmission line `canvhave aV matched terminating impedance, while` the output of the high-.frequency collector I2 feeds directly to the load I3. Under such conditions, the apparatus is in the nature of an amplier. If the outputof the collector I2 is used to energize the transmission line, .thenall ofthe energy gener-v ated may beied through the coupling section to the load I3l-which-is` then 'matched to the transmission line, or only that amount ofy energy necessary to maintain the apparatus in opera-k tion may be diverted from load I3 tothe couplingjsection.Y Under such conditions the apparatus isin the nature of an oscillator. w

Ingeneral, the coupling section II is used for coupling a'wave eld with the electron stream in such a manner as will permit deflectionr of the electron` stream. This application deals with the use ofj'a traveling `wave field for this purpose, butasdisclosed in 'my application of serial #388,-

279,*"1'lled "April 12, 1941 it is also possible to use ccuplerused as an amplifier for high-frequency currents.Y The exciting oscillator 2l] energizes thej transmission line 22.-,23 'of the coupling section',

whichV includes two spaced parallel. conducting members 22 and 23: 'The'electron gun 2I directs a stream of high velocity electronsthrough the coupling section as is indicated by the horizontal dotted lines. The end of the coupling section 22-23 of the transmission line is terminated with a load impedance 26 matched to the characteristic impedance of the coupling section or transmission line. High-frequency energy is collected from the waved electron stream by the collector plates 2l and 28 and the high-frequency collector circuit 2li transfers the energy to the load 25. A ground return circuit to the gun -2| is provided for the current o f the electron stream and electron gun 2i. The tube casing 23 permits evacuation of the air from the region through which the electron stream is directed. The traveling wave is represented graphically by the voltage curve E shown at 3B.

By reference to Figure 2 the operation of the wave coupler as an amplier can be made clear. The coupling section of the transmission line 2,2--13 is energized by the oscillator 2i) and the line so 'terminated by the load 26 as to permit traveling waves to traverse the coupling section iii-23. The electrostatic field set up by the traveling wave between the conductors 22--23 is illustrated graphically by the voltage curve E in graph 30. The transmission line is shown as marked off in one-half wave lengths to correspond with the voltage curve, and the one-half Wave length segments are indicated by the letters a, b, c, d, e, and the remainder f. The primes of the above letters indicate the corresponding regions of the graph. The electron gun 2 i directs s, high velocity stream ci electrons along the straight dotted lines shown. It is possible to make the velocity of propagation of the traveling wave and that of the electrons in the electron stream equal. The voltage curve Si) shows, for a given instant, the distribution of the fields in the traveling wave. It follows that the electrons in the segment a will be in a positive polarity electrostatic field, as indicated by the graph Sil-a'. Also, the electrons in segment b will be in a negative polarity electrostatic iield, as indicated by Sii-b. A similar inference can be drawn for the electrons in the remaining segments of the coupling section. Since the electrons in the segment a move along the line with the same velocity as the positive polarity wave pulse 36-a, the electrons will be displaced more and more in a given direction as they and the wave pulse simultaneously reach successive positions along the line, such as at c and c. The electrons in a negative polarity field, as at band Bil-b', will be displaced in the opposite direction. As a result, the electron stream will be waved into the shape` indicated by the curveddotted line, which, it will be noted, tend's to become graphically similar to the voltage curve- E in the graph Sil. After being waved in the coupling section, the electron stream impinges upon the collector plates 2l and 2S. It will be observed that those electrons that were in the positive polarity field and thus displaced upwards will be collected on the upper plate 2l, while those that were in the negative polarity field will be collected on the lower plate 28. The result will be. to alternately charge the upper and lower plates with electrons, and energize them at a frequency which is proportionate to thenumber of pulses collected per second.

Figure 3 shows a diagram of the wave coupler used as an oscillator. The electron gun is represented by the cathode element 35 and the plate 36, each connected in the conventional manner to energizing sources. The coupling section is formed by the spaced conductor elements 3l` and 38. `The electron stream is collected by the collector plates 39 and. d, and thereby energizes the collection circuit Al. High-frequency energy is fed from the collection circuit 4I through the line l2 to the head of the coupling section 31.-38, the coupling section 3'1-38 being terminated in a matched load 43. A ground return is provided for the electron current. The tube casing M permits the air to be evacuated from the region through which the electron stream is directed.

The operation of the wave coupled oscillator is Vfundamentally the same as that of the amplifier in Figure 2. The variation lies in the use of the generated high-frequency energy collected in circuit 4| for energizing the coupling section 3l.-.-3S. It will be noted that for the high- 'frequency energy to reach the load 43, it must pass from circuit Si through the feed-back line d2 and then through the coupling section 31-38 to the load 43. Hence, all of the energy that is used in the load serves to wave the electron stream while passing through the coupling section 3l-38, and so, with proper time and space phasing, maintains the device in a state of continuous oscillation. in order to stabilize the oscillations at some preassigned frequency, the collection circuit 4i may be tuned to some preassigned frequency by including the proper L. C. circuit elements. In order that oscillations may be sustained, it is necessary that the head of the coupling section 31-38 should be energized in the proper phase. The phase of the voltage delivered to the coupling section 31-38 can be readily controlled by any of the conventional phase shifting devices, and one method, easily applicable to the return transmission line 42, would be to adjust its length. The electron stream is indicated by the dotted lines and is shown in its normal state prior to being waved or deflected by the traveling wave.

Figure 4 shows a traveling wave. coupler used as an oscillator, but in which the coupling section transmission line is depicted as of the coaxial type. The electron gun 5o directs a circular ring of electron streams into the coaxial coupling section of the transmission line which has an outer cylindrical conductor member 5l and an inner conductor member 52. The collector ring plates E3 and 54 collect the highfrequency energy and feed it along the line 5l and 58 to the coupling toroid 6) at the head of the coupling section 5l-52. The high-frequency terminating circuit 55 is shown as of the toroid type; it is preferably matched to the coupling section Eli-52 so as to reduce the setting up of reflected waves. The high-frequency energy in the toroid 55 is coupled to the load 62. The slotted openings 59 in the toroid @il permit the electron stream to be directed into the coaxial coupling section 5I-52. For the purpose of permitting evacuation of any air in the region through which the electron stream is directed, an air tight surface can be formed by the outer coaxial tube and the casing 6i surrounding the electron gun 50. In the drawing, the electron stream is shown by the dotted lines and in its normal state prior to being waved.

The operation of thewave oscillator of Figure 4 is fundamentally similar to that of Figure 3, the main difference being that the traveling wave and its fields are guided by a coaxial line. Highfrequency energy is collected from the electron stream by the ring plate collectors 53 and 5. This energy is fed back to the head of the coupling section '5I-52 by the transmission line 57' and 58, which is shown asof the two wire construction type. Obviously, the return line 51-58 could lbe of coaxial construction also, if desired. If symmetry of construction was desired, it would be possible to have one coaxial line inside of and concentric with the other, one serving as the coupling section, and the other as the return line. In the Figure 4 diagram, the ring collector plates 53 and 54 are placed in the coupling section 5|-52, but if Vdesired could be placed outside the toroid 55'by providing suitable slots in the toroid 55 for the electron stream to pass through, and by enclosing the collector rings in an air-tight casing. One advantage of such a construction would be to simplify the matching of the coupling section 5|-52 to the toroid 55 and the load 62.

The above description serves to illustrate the general principles of the wave coupler when using traveling waves, and particularly as applied to amplifiers and oscillators.v In the illustrated coaxial type of coupling section, it was assumed that a radial pattern of electrostatic field Was being propagated along the coaxial line. Many other patterns or modes are known to the art, and could be used in lieu of the radial pattern, as long as the electrostatic fields thereof can act upon the electron stream to deect it, and if suitable collection means are employed.

For simplicity, it has been assumed that the velocities of propagation of the wave along the transmission line and that of the electron stream were equal, but this is not a necessary restriction. When the wave velocity and the electron velocity are equal, the coupling section can be of any length, and the total displacement of any displaced electron segment will be proportional to the coupling section length and the strength of the displacing eld acting upon the electrons. If the electron Velocity diiers from that of the traveling wave, and the coupling section is long enough to permit a point of one shift one wave length (or an integral number of wave lenghths) with respect to the other, it follows that the positive and negative polarities of the iields acting upon such electrons will in eiiect cancel one another, so that the emerging electron stream will not :be waved. If differing velocities are used, it is preferable that the total shift resulting should not exceed one-half wave length, in order to prevent total or partial cancellation of the effectiveness of the acting elds.

In the coupling sections referred to in the drawing, the dielectric medium separating the conductor members is assumed to be space. However, as long as a path is provided for the electron stream, regions of the separating dielectric can be of material substances, such as of glass. For a given spacing of conductors, the introduction of a glass dielectric would increase the capacity per unit length of the coupling section, and so modify the velocity of the propagated travelingwave. It follows that the glass dielectric used could also serve for the casing of the tube, so that in effect the conductors for the coupling section could be placed outside the tube walls. In some applications of the wave coupler, this form of construction might have physical or technical advantages.

With regard to the particular form that the coupling section may assume, it is to be noted that considerable variation is possible as long as the -basic requirements of an electromagnetic traveling wave having an electrostatic field component capable of deiiecting an electron stream are fullled. If the two wire `transmission line and the electron stream, such as is illustrated in Figure 2, are taken as a basic element, it can be used to trace out other forms, as by displacing it laterally along a line perpendicular to the plane of the basic element pattern, or by revolving it laterally around a given line serving as an axis to create a surface of revolution. In the former case, the coupling section would have the form of two spaced parallel conducting sheets, with a moving sheet or streamof electrons directed between them. In the latter case, if the axis line Was parallel to the transmission line elements and the radius was constant, the coupling section would be similar to the concentric circular cylinders of a coaxial transmission line, substantially as illustrated in Figure 4.

I claim:

1. In a high-frequency generating system including a section of a coaxial transmission line and high velocity charged particles moving in a low pressure region, said coaxial transmission line being adapted to guide an electromagnetic traveling wave along a given, path, means for energizing said section of said coaxial transmission line from a high-frequency energizing source to form a traveling wave having a transverse electrostatic eld component along said path, means for maintaining a low pressure region along said path, means for directing said high velocity charged particles along said path and in the ield of said electromagnetic wave, whereby charged particles of the stream are deflected by elds of the traveling wave, and means for collecting high-frequency energy from the deflected stream of charged particles.

2. In a high-frequency system including a coaxial transmission vline and a stream of high velocity charged particles moving in a low pressure region, said coaxial transmission line comprising at least two dissimilar media adapted to guide an electromagnetic wave along a given path, means for maintaining a low pressure region along said path, means for exciting said coaxial transmission line with high-frequency energy, means for impedance matching at least one end of said coaxial ltransmission line to Ypermit a flow of high-frequency energy along said line in the form of a traveling electromagnetic wave, said electromagnetic wave having an electrostatic field component substantially transverse to said path, means for directing said stream of high velocity charged particles along said path and in the eld of said electromagneticwave, whereby charged particles of the stream are deflected by elds of said wave, and means for collecting high-frequency energy from the deilected charged particles of the stream.

3. In a high-frequency generating system including a section of a coaxial transmission line yand a source of high velocity charged particles .in `a low pressure region, said coaxial transmission line being adapted to guide an electromagnetic wave along a given path, said section of said coaxial transmission line being terminated at each end by va conductive toroidal shell having an annular slot therein, the outer vedge of each toroidal shell being conductively joined to the outer conductor of the said coaxial line, and the inner edge of each toroidal shell being conductively joined to the inner conductor of said coaxial line, one of said toroidal shells having at least one yopening adapted to permit .the directing of a stream of charged lparticles along said path and in the annular space within said coaxial line, two concentric annular collector rings adapted to fit coaxally within said coaxial transmission line and insulated therefrom,4 means for directing said high velocity charged particles along said path toward said collector rings, means for maintaining Ya low pressure region along said path, means for energizing said coaxial transmission line with high-frequency energy, and means for collecting high-frequency energy from said annular collector rings.

4. In a high-frequency generating system including a section of a coaxial transmission line `and a source of high velocity charged particles in la 10W pressure region, said coaxial transmission line being adapted to guide an electromagnetic Wave along a given path, said section of said coaxial transmission line being terminated at each end by a conductive toroidal shell having an annular slot therein, the outer edge .of each toroidal shell being conductively joined to the outer conductor of the said coaxial line, and the inner edge of each toroidal shell being conductively joined to the inner conductor of said coaxial line, one of said toroidal shells having at least one opening adapted to permit the directing of a stream of charged particles along said path and in the annular space within said coaxial line, two concentric annular collector rings adapted to nt coaxially Within said coaxial transmission line and insulated therefrom, means for directing said high Velocity charged .particles along said path toward said collector rings, means for maintaining a low pressure region along said path, means for collecting high-frequency energy from said annular collector rings, means for energizing said coaxial transmission line with said collected high frequency energy, and means for coupling a high-frequency load to one of said toroidal shells.

5. In a high-frequency generating system in- Cludng a section of a -coaxial transmission line and a source of high velocity charged particles in a loW pressure region, said coaxial transmission line being adapted to guide an electromagnetic Wave along a given path, said section of said coaxial transmission line being terminated at each end by a matched resonating chamber, .one of said resonating chambers having at least one opening adapted Ito permit the directing of .a stream `of charged particles along said path .and in the annular space Within said coaxial line, ltvvo substantially concentric annular collector rings adapted to t coaxi-ally Within said coaxial transmission line ,and insulated therefrom, means for energizing said coaxial transmission line with high-frequency energy, means for directing said high velocity charged particles along said path toward said collector rings, means for maintaining .a low pressure region along said path, and means for collecting high-frequency energy from said annular collector rings.

HOWARD M. STROBEL. 

